Unexpected thunderstorms forced NASA to scrub today's planned launch of the shuttle Columbia, delaying the deployment of a $1.6 billion X-ray telescope at least another 24 hours.

It was the second delay in 48 hours for Columbia's crew, led by NASA's first female shuttle commander, Eileen Collins, and a bitter disappointment to astronomers who have labored for more than two decades to get the Chandra telescope into orbit.

Collins, pilot Jeffrey Ashby, Catherine "Cady" Coleman, flight engineer Steven Hawley and Frenchman Michel Tognini were grounded this morning by weather just five minutes before the scheduled 12:28 a.m. liftoff. NASA extended the launch window, but when the storms did not clear, the flight was scrubbed at 1:18 a.m.

First lady Hillary Rodham Clinton and her daughter Chelsea, a delegation of female members of Congress and the co-captain of the U.S. women's soccer team were on hand again this morning for the second try. The astronauts had attempted to take off Tuesday morning, but that countdown was manually stopped at T-minus seven seconds -- a half-second before main engine ignition -- when high levels of explosive hydrogen gas were detected in the shuttle's engine compartment.

As it turned out, one of two hazardous gas detectors had merely "burped" a bit of hydrogen back into the detector, a phenomenon that randomly occurs from time to time. There was no leak, and Columbia could have been safely launched.

But the high reading occurred at the worst possible time, at T-minus 16 seconds, and operator Ozzie Fish could not afford to wait for a second reading at T-minus 8 seconds to confirm the presence of a leak.

Had he done so, Columbia's main engines would have started igniting before the countdown could have been stopped.

"Had we started the engines, we wouldn't be here today talking about a launch tonight," said Grant Cates, the engineer in charge of Columbia's ground processing. "We'd be talking about a launch in August. We would have had at least three weeks, probably more, to turn these engines around and go fly this mission."

If Columbia cannot blast off on a third attempt, scheduled for 12:24 a.m. Friday, it must wait until at least Aug. 12.

On the first attempt Tuesday, Fish ordered a countdown cutoff at T-minus 9 seconds, and Barbara Kennedy, operating a countdown computer called the ground launch sequencer, issued the shut-down command at T-minus 8 seconds.

The countdown actually stopped one second later.

Cates and other NASA managers praised Fish and Kennedy for reacting so quickly and preventing a potentially major launch delay. Even though the data were erroneous, Cates said, Fish did exactly what he should have done given the situation.

"It was an incredibly unfortunate coincidence that it occurred at that point where we didn't have time to get another reading before the engines started," Cates said.